Prior to performing compensation, the user needs to import result files (DYNAIN format) of deformed sheet metal part before and after springback. The tool mesh of last forming step (if this is the first springback compensation, import the original tool mesh) is required for springback compensation. If the desired blank shape cannot be obtained after first compensation, several iterations may be performed to compensate the tooling. Springback compensation dialog box is illustrated in Figure 9.1.1. Click on each icon in the dialog box to import or assign the part. The color selected icon will be changed from red to green if the part is defined.
Figure 9.1.1 Springback Compensation dialog box
BLANK INPUT
This field enables the user to import deformed parts (before and after springback) and assign parts for springback compensation.
BEFORE SPRINGBACK
Import or select the blank model before springback. The user can import file in dynain format.
AFTER SPRINGBACK
Import or select the blank model after springback. The user can import file in dynain format.
DESIRED SHAPE
Import or select the desired blank shape. The user can import file in dynain format. It is usually the shape before springback.
COMPENSATED SHAPE
Import or select the compensated blank shape. The user can import file in dynain or *.tmp format. In first springback compensation iteration, it is the blank shape before springback. In second and subsequent iterations, the user should import disp.tmp file for the compensated part and define it as the compensated blank shape.
TOOL INPUT
MASTER TOOLS
Import or select master tools. The user can import file in *.nas or *.new format.
SLAVE TOOLS
Import or select slave tools. The user can import file in *.nas or *.new format.
ZONE
ALL
Select all regions of part for springback compensation.
LOCAL
Select local regions of part for springback compensation.
INNER
Use curve tool to define a region. If INNER option is selected, part area insider the curve will be compensated. If INNER option is not selected, part area outside of curve will be compensated. The user can click on CURVE button to define curve.
PARAMETERS
Compensation parameters consist of METHOD, SMOOTH LEVEL, SCALING FACTOR, ELEMENT REFINEMENT AND UNDERCUT AVOIDANCE. Refer to LS-DYNA User’s Manual for detailed description of each parameter.
METHOD
LS-DYNA provides 8 methods for springback compensation. The recommended methods are 7, 3 and 6, and the other methods are seldom used. Each method has its advantages and disadvantages. The three commonly used methods are described below:
Method 7
This is a non-linear method and the iterative method is used. If the punch is chosen as the master side, the binder will not be changed. The only change occurring involves inside punch opening. Under this option, the smoothing factor has little effect. The smoothness of the modified tool depends on the magnitude of the springback and the size of the addendum region.
Advantages: The binder will not be changed.
Disadvantages: The change will be limited inside the addendum region, and the modified surface may not be smooth if the springback magnitude is large and the transition is small.
Method 6
This is a non-linear method and the iterative method is used. The smoothness and the transition region of the modified surface will depend on the springback magnitude and the smoothing factor. If the springback magnitude is large, the transition region will be increased automatically. On the other hand, the transition region will be smaller if the springback magnitude is small. At the same time, a larger smoothing factor will result in a smaller transition region.
Advantages: The smoothness of the modified surfaces can be controlled.
Disadvantages: It is impossible to limit the transition region, and the binder surface could change if the springback is large.
Method 3
Similar to Method 6, however, it is a linear method.
SMOOTH LEVEL
The smooth level parameter controls the smoothness of the modified surfaces. A large value makes the surface smoother. The commonly used value is between 5 and 10. If springback is large, the transition region is expected to be large. However, by using a smaller value of smooth level, the region of transition can be reduced.
SCALING FACTOR
The scales how much of the shape deviation is compensated. If this factor is appropriate, the user can obtain the desired result with only a few repeated calculations. Otherwise, plenty times of modification are required. The product of this scaling factor and springback quantity is the compensation quantity for reverse direction. The default is 0.75.
ELEMENT REFINEMENT
Refine the tool mesh.
UNDERCUT
Automatically check the element with undercut generated after springback compensation.
BATCH OUTPUT
This function allows the user to output a series of input decks with different scaling factors. The input decks are stored in different folders. If this option is activated, the user can key the range and increment of scaling factor.
SUBMIT
After all parameters are defined, the user can click on SUBMIT button to display the SUBMIT JOB dialog box illustrated in Figure 9.1.2. Refer to the relevant sections for description about methods for submitting jobs.
Figure 9.1.2 Submit Job dialog box
EXIT
Exit springback compensation dialog box.